JP2001-248449A describes a power transmission device that transmits a rotation power of a motor to a shaft of a valve device. The valve device has a valve supported by the shaft so as to control intake air.
As shown in FIG. 9, the power transmission device includes a worm gear (not shown) fixed to an output shaft of the motor, a helical gear 101 meshing with the worm gear, a spur gear 102 located coaxially with the helical gear 101, and an output gear (not shown) meshing with the spur gear 102. An impact absorbing member has a first plate 103, a second plate 104 and a rubber portion 105, and is disposed between the helical gear 101 and the spur gear 102, to rotate integrally with the helical gear 101 and the spur gear 102.
The rubber portion 105 is inserted between the first plate 103 and the second plate 104, and is vulcanized-bonded to the first and second plates 103 and 104. The rubber portion 105 is twisted in use. Thus, a deformation amount of the impact absorbing member increases, so that an impact absorbing performance is ensured. Therefore, a lock of the worm gear can be prevented by the twisting effect of the impact absorbing member when the valve bumps into a fully-close stopper.
However, in this case, the number of components and assembly man-hours are large. As a result, production cost becomes high. Further, positioning deviation may be generated among the components.